Oxidation catalyst and process

ABSTRACT

CATALYSTS CONTAINING MANGANESE MOLYBDATE, TELLURIUM OXIDE AND A MANGANESE PHOSHATE ARE USEFUL IN CONVERTING PROPYLENE OR ISOBUTYLENE IN THE PRESENCE OF OXYGEN TO MIXTURES OF ACROLEIN AND ACRYLIC ACID OR METHACROLEIN AND METHACRYLIC ACID.

US. Cl. 252-437 4 Claims ABSTRACT OF THE DISCLOSURE Catalysts containing manganese molybdate, tellurium oxide and a manganese phosphate are useful in converting propylene or isobutylene in the presence of oxygen to mixtures of acrolein and acrylic acid or methacrolein and methacrylic acid.

This invention relates to new and useful catalysts and to a method of preparing unsaturated aldehydes and unsaturated carboxylic acids by oxidation of unsaturated hydrocarbons at an elevated temperature.

The invention relates more particularly to catalysts comprising manganese molybdate, tellurium oxide and manganese phosphate in a molar ratio of 100 MnMoO 10- 100 TeO and 5-50 MIlgPzOq and to a method of preparing acrolein, methacrolein in high yields along with acrylic acid or methacrylic acid by passing vapors of propylene or isobutylene and an oxygen-containing gas over the catalyst at a temperature of from about 325 C. to about 550 C. The catalyst can also be designated as MnMO TE1 0M1'12 30P2 20039 120 P in the form of a phosphate, i.e. each P atom is attached to 3 to 4 oxygen atoms.

In my copending applications there are disclosed catalysts having long life that will convert a substantial amount, more than 50% per pass, of a gaseous monoolefin such as propylene or isobutylene to yield acrolein, methacrolein and acrylic acid or methacrylic acid. The catalyst of Ser. No. 485,795 contains M00 TeO and MnP O and provides high yields of acrylic acid. The catalyst of Ser. No. 483,802 contains MnMo TeO and contains phosphorous oxides. This catalyst also provides high yields of acrylic acid. I have now found, quite unexpectedly, that when a catalyst containing MnMoO TeO and Mn P O is used to oxidize olefins, that at equivalent temperatures much higher yields of acrolein are obtained than with either of these two catalysts. Mol percent efficiencies of about 45 to about 55 for the aldehyde are obtained with the catalyst and process of this invention wherein manganese is present both as a molybdate and phosphate.

Fly

The reactants are (l) propylene or isobutylene and (2) an oxygen-containing gas, which can be pure oxygen, oxygen diluted with an inert gas, oxygen enriched air or air without additional oxygen. For reasons of economy, air is the preferred oxygen-containing reactant.

For the purpose of this invention the hydrocarbons which are oxidized can be defined generically by the formula wherein it is also apparent that the end products formed result from the oxidation of only one methyl group on the hydrocarbon molecule while the terminal CHg remains intact.

Stoichiometric ratios of oxygen to olefin for the purpose of this invention are 1.5 to 1. The molar ratio of oxygen to olefin should be at least 2 to 1. Slightly lower amounts of oxygen can be used at a sacrifice of yield. There is no critical upper limit but when air is used, large excesses will require large equipment investment. It is preferred to use 33 to 66% excess oxygen. A useful range is 1.5 to 4 mols of oxygen per mol of olefin. Larger excesses do not impair the yields of aldehydes and acids,

- but for practical considerations an excess much above would require extremely large equipment for a given production capacity.

The addition of steam into the reactor along with the hydrocarbon and oxygen-containing gas is desirable but not absolutely essential. The function of steam is not clear, but it seems to reduce the amount of carbon monoxide and dioxide in the efiluent gases.

Other diluent gases can be used. Saturated hydrocarbons such as propane are rather inert under the reaction conditions. Nitrogen, argon, krypton or other known inert gases can be used as diluents if desired but are not preferred because of the added cost.

There are several methods for the preparation of the catalyst, which can be supported or unsupported. It is possible to dissolve each of the starting ingredients in water and combine them from the aqueous solutions or the ingredients can be dry blended. Because of the more uniform blend obtained by the solution procedure, it is preferred.

A general procedure for preparing a catalyst is to provide the requisite amount of a manganese molybdate in water, a tellurium compound and a manganese salt in water. Add the requisite amount of phosphoric acid to the manganese salt solution. Add the tellurium compound to the manganese molybdate and then add the manganese salt-phosphoric acid mixture to the manganese molybdatetellurium mixture. The catalyst is then dried and baked at 400 C. for about 16 hours.

Supported catalysts can be prepared by adding an aqueous slurry of the support to the aqueous solution of catalyst or the aqueous catalyst ingredients can be added to the slurry of the support.

Alternately a slurry of the catalyst ingredients can be prepared in water, then dried and baked. For supported catalysts the aqueous slurry of the catalyst ingredients 3 can be added to an aqueous suspension of the support or vice versa, and then dried and baked.

Another method is to blend the dry ingredients and then mix them thoroughly. The main difiiculty is to obtain thorough blending and uniform particle size.

A specific procedure for making the catalysts is as follows:

(a) Slurry 1 mol of manganese molybdate in water.

(b) Slurry 89.2 g. of ammonium tellurate in water.

tures to obtain the yields of desired products obtainable at higher temperatures. About 425 C. in the propylene oxidation some of the desired end products appear to be oxidized to carbon oxides. This is much more apparent at 450 C. For isobutylene, the preferred range is 300 to 450 C.

The molar ratio of steam to propylene or isobutylene can range from to about 5 to 7 or more, but best results are obtained with molar ratios of about 3 to 5 per mol Add the tellurium slurry to the molybdate slurry. to of olefin and for this reason are preferred.

(c) Dissolve 65.31 g. of MnCl Al-i O in water and add The contact time can vary considerably in the range 38.1 g. of 85% H PO Add this mixture slowly to the of about 2 to 70 seconds. Best results are obtained in a molybdate-tellurate slurry. Dry the mixture on a steam range of about 8 to 54 seconds and this range is preferred. bath and bake for 16 hours at 400 C. Thereafter the Longer contact times usually favor the production of acid catalyst is ground to a mesh size of 10-18 and sieved. at any given temperature.

For supported catalysts, suitable supports are silica, The reaction can be run at atmospheric pressure, in silica-containing materials such as diatomaceous earth and a partial vacuum or under induced pressure up to 50-100 kieselguhr, silicon carbide, clay, aluminum oxides and even p.s.i. Atmospheric pressure is preferred for fixed bed syscarbon, although the latter tends to be consumed during tems and a pressure of 1 to 100 p.s.i. for fluid bed reacthe reaction. If the catalyst is to be supported the aquetions. Operation at a pressure which is below the dew ous solution or slurry of ingredients can be added to an point of the unsaturated acid at the reaction temperature aqueous slurry of the support or vice versa, prior to dryis advantageous. ing. The procedure after drying is the same as that already The data in the examples show yields in percentages of described. Thus, to the aqueous catalyst ingredients 240 unsaturated aldehydes and acids that can be obtained with g. (1.2 mols) of a 30-35% aqueous colloidal dispersion a single catalyst, using fixed ratio of reactants but changof microspheroidal silica (Ludox HS.) are added slowly ing the temperature and/or contact time. Further varia- With stirring. Stirring is continued for about /2 hour prior tion is obtainable by controlling the other variables in the to drying. Another procedure is to add the mixture dereaction including the catalyst compositions within the scribed under (c) to the Ludox and then add the requisite limits set forth herein. amount of TeO and M00 as a slurry. Also the ingredi- The examples are intended to illustrate the invention ents can be added to the Ludox individually if desired. but not to limit it.

Another method is to grind MnMoO TeO and a manganese phosphate to the proper particle size and then THE EXAMPLES thoroughly mix the dry powders. The mixture can be added to an aqueous slurry of a support or vice versa genes of runs Was made in a fixed bed reactor Ofhlgh and thereafter dried and baked 511K323. (Vycor) glass tube 12 inches long and 30 mm. outer For fi d bed systems a 0 1 mesh s Sieve) siz diameter. The reactor had three inlets, one for air, one is satisfactory. For fluid bed systems the catalyst particle for Steam and one f P 'Ppy Thffie external elfictfi- Size should be g mesh s Sievc) cally operated heating coils were wound on the reactor.

The exact chemical structure of the catalysts made by 40 one of the Coils @Xtended along the entire length of the the above procedures is not known, but catalysts with reactor and each of the remaining Coils extended y molar ratios of 100 MnMo, 10-100 Te and 5-100 of MnP about one half th length of the reactorcan be used for converting the monoolefinic hydrocarbon Outlet Vapors f Passed lhrough Short Water: to a nitrile. The catalyst contains chemically bound oxygen cooled condenser- UHCOndEmSF-d gasfis Were Passed througn so that the generic formula can be Written as a gas chromatograph (Perkm-Elmer model 154D) and analyzed continuously. The liquid condensate was weighed MnMO4 100Te02 IOAOOMHZPZO? and then analyzed for acrylic acid and acrolein in the gas The phosphate can be a P0; radical, pyrolphosphate or Chromatographa polyphosphate, for example, manganese orthophosphate r The reactor was filled to about of its capacity (ous), pyrophosphate, monohydrogen orthophosphate do with 170 ml. of a catalyst made by the solution method (ous) and dihydrogen orthophosphate (ous), and metadescribed above, having a ratio of MnMoO 33 T e0 phosphate (i) and 16.5 Mn P O The catalyst was not supported and A preferred catalyst is one having a ratio of about hadamesh size of 10-18 (U.S. Sieve). 100 MnMoO 33 TcO and 10-30 Mn l O because it Steam at a temperature of ZOO-250 C. was first passed gives a high yield of desired products, and the preferred into the reactor. Then propylene and air were separately support is silica, because of its low cost and good fluidizfed into the stream of water vapor. This mixture then ing characteristics. passed through a preheater and entered the reactor at The reaction temperature can range from about 300 to about 200-250 C. The reactor was preheated to about 500 C. for the oxidation of propylene but the preferred 6O 285 C. before the gas feed was begun. range is from about 325 to about 425 C. Below 325 C. The ratio of reactants per mol of propylene, oxygen, the conversion per pass is lower than. desirable and low steam, cold contact time in seconds, and temperature are temperature tends to produce more aldehyde than desired. shown in the table below. The table summarizes the data Usually, a longer contact time is needed at lower temperaobtained in these runs:

M01 percent yield on- Contact M01 percent Oxygen, Temp, Steam, time, propylene. Propylene Converted mols 0. mols seconds converted Aer. AA

4 350 4. 2 4s. 5 87. an 63. 10 20. 70 :5 365 4.01; in 02. as so. an 28. 51 3 am 4.01; 40 its. on 45. 40 33. 33 3. or 34s 4. 2 00 26.31

I claim: References Cited 1. A catalyst composition consisting essentially of man- UNITED STATES PATENTS ganese molybdate, tellurium oxide and a manganese phosphate in a molar ratio of 100 manganese molybdate, 10- 3228890 1/1966 Eden 252*437 100 tellturium oxide and 5-50 manganese phosphate. 5 3383330 5/1968 Kang 252*437 2. The catalyst of claim 1 wherein the manganese phos- 3502069 4/1970 Eden hate is man anese p rophosphate. p 3. The cat lyst of Zlaim 2 wherein the catalyst contains PATRICK GARVIN Pnmary Exammer 100 MnM0O about 33 TeO and 1030 Ml'lzPzOq. s CL 4. The composition of claim 3 wherein there is about 10 260 533 U, 604 16.5 MIlgPgOq. 

